Efforts to shape the future in prevention, diagnosis, and treatment of lung disease will, in part, depend on the generation of specific genetic markers capable of distinguishing and characterizing individual lung tumor subtypes. Such genes or markers might then aid in disease management by assessing survival, predicting response to therapeutic approaches, or more importantly, assist in identifying areas of premalignant change. A screen of several non-small cell lung carcinomas (NSCLC) using Differential Display PCR (DDPCR) identified a gene fragment, DAL-1, with decreased expression in one such adenocarcinoma. Further examination revealed this gene's level of expression was diminished or lacking in 59% of primary NSCLC (22/37) and 8/9 (89%) NSCLC cell lines. The expression of this gene was also lost in various other cell lines including MCF-7 (breast) and RKO (colon). The cDNA and protein sequence of DAL-1 reveals a differentially spliced gene with a glycophorin-like binding domain and a long hydrophilic carboxy-terminal tail, suggesting it may play a role in tumorigenesis by operating at the cellular membrane surface. It Is the overall goal of this study to ascertain the role DAL - 1 plays as a tumor suppressor gene for lung cancer and investigate it's feasibility as a genetic and clinical marker for lung cancer or tumorigenesis in general. Specifically this proposal examines (1) the effect of DAL-1 re-expression on growth, soft agar colony formation, apoptosis, migration, cell cycle kinetics, and tumorigenicity in nude mice, (2) the function and cellular location of DAL-1 protein and it's alteration in lung cancer, (3) the molecular and clinical disease parameters correlating with loss of DAL-1 expression, (4) the frequency and specificity of loss of heterozygosity (LOH) as it occurs around DAL-1, (5) the genomic structure of DAL-1 and its mRNA splice variants in normal and tumor tissue, and (6) the frequency and type of DAL-1 coding mutations occurring as a result of tumorigenesis. This work is expected to establish DAL-1 as a novel and important tumor suppressor gene as well as a genetic biomarker for lung cancer, and potentially a variety of other tumors as well.